Spring with a mass at an angle, need original length of spring

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SUMMARY

The discussion revolves around calculating the original length of a spring attached to a 5 kg mass on a 45-degree incline, with the spring constant specified as k = 20 N/m. The user initially calculated the forces acting on the mass and derived an extension of the spring, resulting in a contradiction where the unstretched length appeared negative. The key equations utilized include Hooke's Law (F = k(λx)) and trigonometric functions to resolve forces. The user seeks clarification on their calculations and the validity of the problem setup.

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  • Understanding of Hooke's Law (F = k(λx))
  • Basic trigonometry for resolving forces on inclined planes
  • Knowledge of free body diagrams for analyzing forces
  • Familiarity with equilibrium conditions in physics
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  • Review the principles of Hooke's Law and its application in spring systems
  • Learn how to construct and analyze free body diagrams for complex systems
  • Study the effects of angles on force components in inclined planes
  • Explore problem-solving techniques for equilibrium in mechanical systems
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Students studying physics, particularly those focusing on mechanics and spring dynamics, as well as educators seeking to clarify concepts related to forces on inclined planes and Hooke's Law.

2Dark4u
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Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.
 

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2Dark4u said:

Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.

I wonder if k was supposed to equal 20 kN/m
 
correction ! sorry
 
Draw a Free Body Diagram for the 5 kg block.

attachment.php?attachmentid=45157&d=1331882305.jpg
 
Ive checked with everybody. And so far what people have been able to tell me is that it just looks like the question has to be wrong

I did draw the diagram, its how i saw were all the forces were going. Unless I messed it up somehow.
 
Last edited:

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